The official spoke on condition of anonymity because of the ongoing investigation.
Autopsy results showed he died from an accidental overdose of fentanyl, a synthetic drug 50 times more powerful than heroin. Deputies attempted CPR but efforts to revive him were unsuccessful.
According to a search warrant issued on April 21 a year ago - the day Prince was found dead - investigators found several pills labeled "Watson 853".
Search warrants and other documents related to criminal cases are normally public record, but authorities had requested all documents related to the Prince death investigation be sealed as the probe proceeded.
Prince did not have a cellphone, and authorities searched multiple email accounts that belonged to him, as they tried to determine who he was communicating with and where he got the drugs that killed him, according to the search warrants.
Schulenberg was among those who arrived at Paisley Park after the singer's body was found in an elevator inside the complex, according to the documents.
He says authorities could charge Dr. Michael Todd Schulenberg and Prince's friend, Kirk Johnson, with a low-level felony that wouldn't result in prison time.
April 20, 2016: Schulenberg treats Prince again.
On Monday, search warrants executed by local authorities are due to be unsealed, likely including one from the first search of Paisley Park. Watson 853 is an imprint on generic pills that contain acetaminophen and hydrocodone bitartrate.
It has been reported vitamin bottles were also found throughout Prince's home during the inspection. The bottle contained 10 white pills with the inscription A-349 and one orange pill with the inscription No. 8.
And now, never-before-seen search warrants have revealed that officers searching the Purple Rain singer's home found that it was littered with containers of different pills.
The specialist, Dr. Howard Kornfeld, couldn't get there immediately so he sent his son, Andrew Kornfeld, on an overnight flight to Minnesota.
Judith was with Prince just days before his death. The goal was for the younger Kornfeld to help evaluate Prince's health and encourage him to enter treatment for pain management and potential addiction issues, attorney William Mauzy told reporters. He said he was there on behalf of his father's recovery clinic called Recovery Without Walls to see if Prince would qualify and be interested in their program.
KIRK JOHNSON'S PRESCRIPTION PICK-UPS: According to court documents, Kirk Johnson went to Walgreen's and picked up Prince's prescription medication, prescribed in his name.
FILE - In this April 21, 2016, file photo, a rainbow appears over Prince's Paisley Park estate near a memorial for the rock superstar in Chanhassen, Minn. Investigators found no prescriptions for fentanyl in Prince's name. The prescribing doctor was listed as Schulenberg.
Some pill bottles had Prince's long-time friend and estate manager Kirk Johnson's name on them.
About a week before his death, Prince's private jet made an emergency landing early April 15 in Moline, Illinois, on the way back from a performance in Atlanta.
Many pills were inside a suitcase with the name tag "Peter Bravestrong" - an alias used by the singer.
PRINCE DIDN'T OWN A CELL PHONE: One of Prince's bodyguards told investigators that Prince had once owned a cell phone, but that after his cell phone was hacked into and a lot of his personal information was stolen, "Prince became leery of storing his information on the phone and stopped carrying a cell phone and began sending emails".